Turbulence / free surface interaction produces key phenomena - anisotropic near-surface turbulence

Watermark - Vortex structure and free surface deformation (DNS calculation)

•Turbulent production dominated by the generation of wall ejections, formation of spanwise “upsurging vortices”

•Upsurging vortices reach free surface, form surface deformation patches, roll back in form of spanwise “downswinging vortices”, with inflow into the bulk.

•The ejection - inflow events are associated with the deformation of the free surface and a redistribution of near surface vorticity and velocity fields.

Conceptual illustration of experimental observation of burst-interface interactions - From Rashidi, Physics of Fluids, No.9, November 1997.

CHALLENGE: MAGNETOHYDRODYNAMICS•Complex non-linear interactions between fluid dynamics and electrodynamics

•Powerful mechanism to “influence” fluids

•Strong drag effects, thin active boundary layers, large (possibly reversed) velocity jets are characteristic MHD phenomena

•Large currents with joule dissipation and even self-sustaining dynamo effects add to computational complexity

FLO W

Free surface flow velocity jets produced from MHD interaction - UCLA calculation

Computational Challenge Li flow in a chute in a transverse field with: b=0.1 m (half-

width); B0=12 T (field)

000,100

Ha = B0b mHab

Ha610

Each cross-section requires MANY uniform grids, or special non-uniform meshes.

102 10)/( Hab

MHD interactions can change the nature of turbulence - providing a lever of CONTROL

From Dresden University of Technology

Experimental control of flow separation by a magnetic field:

fully developed von Kármán vortex street without a magnetic field (upper)

with a magnetic field (right)

•Applied Lorentz forces act mainly in the fluid regions near the walls where they can prevent flow separation or reduce friction drag by changing the flow structure.

•Because heat and mass transfer rely strongly on the flow structure, they can in turn be controlled in such fashion.

Flow direction

NEW PHENOMENA IN LM-MHD FLOW2D Turbulence

LM free surface images with motion from left to right - Latvian Academy of Science Data

3D fluctuations on free surfaceN=0

Surface fluctuations become nearly 2D along fieldN=6

Surface fluctuations are nearly suppressedN=10B

SOME PROPERTIES OF 2-D MHD TURBULENCE:

Inverse energy cascade;Large energy containing vortices;Low Joule and Viscous dissipation;Insignificant effect on the hydraulic drag.

2-D turbulence could be very useful as a mean of intensifying heat transfer.

B

EXPERIMENTSunderway at UCLA for near

surface turbulence and interfacial transport

measurements

DNS and Experimental data are used at UCLA for characterizing free surface MHD turbulence phenomena and developing closures in RANS models

D N Sfor free surface MHD flows

developed as a part of collab-oration between UCLA and

Japanese Profs Kunugi and Satake

Joule Dissipation

0 40 80 120 160y+

-0.008

-0.004

0

0.004

0.008

0.012

D +

0

1

2

3

4

K +

D I

D II

K

Our Science-based CFD Modeling and Experiments are Utilized to Develop Engineering Tools for LW Applications

0 .7 5 0 .8 0 0 .8 5 0 .9 0 0 .9 5 1 .0 0y / h

0

1 0

2 0

3 0

Turb

ulen

t Pra

ndtl

num

ber

- R e= 1 3 0 0 0 - 1 7 9 0 0 - 2 0 2 0 0 - 3 2 1 0 0

1

21 - P r_t for a sm ooth surface (from experim ental da ta)

2 - P r_t for a wavy surface (expected)

12 Turbulent Prandtl Number

Curve1: Available Experimental Data- Missing 0.95-1 and restricted to smooth surface, non-MHD flows

Curve2: “Expected” for wavy surface

Extend RANS Turbulence Models for MHD, Free

Surface FlowsK-epsilonRST model

•Strong redistribution of turbulence by a magnetic field is seen. •Frequency of vortex structures decreases, but vortex size increases.•Stronger suppresion effect occurs in a spanwise magnetic field•Free surface approximated as a free slip boundary. Work proceeding on a deformable free surface solution.

A BIG STEP FORWARD - (1st FREE SURFACE, MHD TURBULENT DNS)

“DNS of turbulent free surface flow with MHD at Ret = 150” - Satake, Kunugi, and Smolentsev, Computational Fluid Dynamics Conf., Tokyo, 2000

Ha=20, Streamwise

Ha=0

Ha=10, Spanwise

0 1 2 3 4 5(Ha/R e) x 1000

0

4

8

12

Cf x

100

0

Experim ent :Re=29000Re=50000Re=90000ca lcu lations

"transition"Ha/R e=1/225

"lam inar"C f=2H a/R e

Comparison of UCLA modelto experimental data

MHD DEPENDENT TURBULENCE CLOSURES

Magnetic fielddirection

Kem em 3C 4C

Streamwise KBC 203

2

04 BC 0.02 0.015

Wall-normal KBC 203

2

04 BC }0.1exp{9.1 N }0.2exp{9.1 N

Spanwise KBC 203

2

04 BC }0.1exp{9.1 N }0.2exp{9.1 N

MHD K- TURBULENCE MODEL

;])[(

Pr

2

nDissipatio

Kem

Diffusion

jK

t

j

oduction

j

it

jj x

Kxx

vxKv

tK

.])[( 2

2

1

emj

t

jj

it

jj K

Cxxx

vK

Cx

vt

tttt

tpnpt n

TCvtCq /Pr;Pr

''

Extending the state-of-the-art in RANS with MHD and free surface effects

1.5-D MHD K- Flow Model• unsteady flow• height function surface tracking • turbulence reduction near surface is

treated by specialized BCs• effect of near-surface turbulence on

heat transfer modeled by variation of the turbulent Prandtl number

Remarkable Progress on Small-Scale Experiments with Science, Education, and Engineering Mission

Two flexible free surface flow test stands were planned, designed, and constructed at UCLA with modest resources in less than a year

Purpose:

Investigation of critical issues for liquid wall flow control and heat transfer

M-TOR Facility

For LM-MHD flows in complex geometry and multi-component magnetic field

FLIHY Facility

For low-conductivity fluids (e.g. molten salt) flow simulation (including penetrations) and surface heat and mass transfer measurement

Our Experimental Approach1. Cost Effective- M-TOR built with recycled components, mostly by

students- FLIHY dual use with JUPITER-II funds from Japan2. Science-Based Education Mission- Several MS and Ph.D student theses- Scientists from outside institutions3. Collaboration among institutions- UCLA, PPPL, ORNL, SNL4. International Collaboration- JUPITER-II (Tohoku Univ., Kyoto Univ., Osaka Univ.,

etc.)- Several Japanese Professors/Universities participate- IFMIF liquid target

Exploring Free Surface LM-MHD in MTOR Experiment

•Study toroidal field and gradient effects: Free surface flows are very sensitive to drag from toroidal field 1/R gradient, and surface-normal fields

•3-component field effects on drag and stability: Complex stability issues arise with field gradients, 3-component magnetic fields, and applied electric currents

•Effect of applied electric currents: Magnetic Propulsion and other active electromagnetic restraint and pumping ideas

•Geometric Effects: axisymmetry, expanding / contacting flow areas, inverted flows, penetrations

•NSTX Environment simulation: module testing and design

MTOR Magnetic Torus and LM Flowloop:Designed in collaboration between UCLA, PPPL and ORNL

Ultrasonic Transducer Plots

-2.4 1.2

4.8

8.4

12.0

15.7

19.3

22.9

26.5

30.1

33.7

37.3

40.9

44.5

48.1

51.8

55.4

59.0

62.6

66.2

69.8

73.4

77.0

80.6

84.2

87.9

91.5

95.1

Microseconds

Without Liquid Metal With Liquid Metal

Timeof-flight

Interfacial Transport Test section length = 4 m

FLIHY is a flexible facility that serves many needs for Free-Surface Flows

KOH Jacket

KOH

Twisted-Tape

3D LaserBeams

ThinPlastic

JUPITER-IIUS-Japan Collaboration on Enhancing Heat Transfer

Flow ControlPenetrations (e.g. modified back wall topology)

Free Surface Interfacial Transport

- Turbulence at free surface- Novel Surface Renewal Schemes

• Large scale test sections with water/KOH working liquid

• Tracer dye and IR camera techniques

• PIV and LDA systems for quantitative turbulence measurements

1.4 cm45 o

Fin

Surface Renewal (e.g. Delta-Wing” tests)

Flow Direction

Dye Diagnostics for Interfacial Mass Transport Measurements

Profile of dye penetration (red dots)

Local free surface (blue dots)

flow direction ~2 m/s

Water jet

hot droplets

Hot droplet penetrating jet

Dynamic Infrared measurements of jet surface temperature

Impact of hot droplets on cold water jet (~8 m/s) thermally imaged in SNL/UCLA test

Liquid lithium limiter in CDX-U

Processes modeled for impurity shielding of core

- Multi-faceted plasma-edge modeling validation with data from experiments

- Experiments in plasma devices (CDX-U, DIII-D and PISCES)

Plasma-Liquid Surface Interactions

Validated Plasma Edge Models were extended to predict the Physics Limits on LW Surface Temperature

Flowing LM Walls may Improve Plasma Stability and Confinement

Several possible mechanisms identified at Snowmass…

• Plasma Elongation > 3 possible – with > 20%• Ballooning modes stabilized• VDE growth rates reduced, stabilized with existing technology• Size of plasma devices and power plants can be substantially reduced

High Poloidal Flow Velocity (Kotschenreuther)• LM transit time < resistive wall time, about ½ s, poloidal flux does not penetrate• Hollow current profiles possible with large bootstrap fraction (reduced recirculating

power) and EB shearing rates (transport barriers)

Hydrogen Gettering at Plasma Edge (Zakharov)• Low edge density gives flatter temperature profiles, reduces anomalous energy

transport• Flattened or hollow current density reduces ballooning modes and allowing high

Presence of conductor close to plasma boundary (Kotschenreuther) - Case considered 4 cm lithium with a SOL 20% of minor radius

SNOWMASS